Documentation: document the semantic diff variables
Documentation: document the semantic diff variables

keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,SimVascular/VTK,SimVascular/VTK,sumedhasingla/VTK,sumedhasingla/VTK,sumedhasingla/VTK,SimVascular/VTK,keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,sumedhasingla/VTK,SimVascular/VTK,sumedhasingla/VTK,SimVascular/VTK